MEW260 Myford Cross Slide Nut

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MEW260 Myford Cross Slide Nut

This topic has 19 replies, 11 voices, and was last updated 31 October 2017 at 02:14 by Chris Trice.

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30 October 2017 at 10:35 #324413
norm norton
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@normnorton75434
This was an article I appreciated seeing, that showed a simple nut and spring used to virtually remove the backlash from a Myford Super 7 cross slide screw and handle. The extra, bronze, nut engaged in the Myford alloy nut with an Oldham (key and slot) coupling and a spring and tube ran over the feedscrew to apply pressure to the bronze nut. This pressure means that (all) free play is removed and only the play in the Oldham coupling can be felt at the handle.

I liked the idea and thought about it. But how firm should the spring pressure be? I then realised that when you rotate the handle anti-clockwise and withdraw the cross slide it is just the pressure of the spring that acts on the bronze nut and thread to move the slide.

Thus, if you applied pressure on a tool for an internal boring cut then one (initially) only had the pressure that the spring could apply. Is this a bad thing? How much pressure does a tool need to cut, and if this is applied by a spring might the tool 'bounce' as it applies a cut?

Clearly, the best idea is to have a split nut with some form of mechanical adjustment to remove the free play. But then this has to be adjusted for the non-worn portion of feedscrew.

I apologise to Mr Warren Jacobs, who wrote the article, if this appears critical as I do appreciate his contribution, and I agree that it must be an improvement. But what do others think of a spring loaded nut as opposed to a mechanically split nut, assuming it would even be possible to design one for a Myford cross slide?

Norm.
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30 October 2017 at 10:35 #38448
norm norton
Participant
@normnorton75434
removing backlash with a spring
30 October 2017 at 11:31 #324422
Michael Gilligan
Participant
@michaelgilligan61133
That got me thinking, Norm.

In my opinion: Any form of anti-backlash nut can only work 'perfectly' on a 'perfectly pitched' screw … Anything that self-adjusts to follow the errors in the screw will be a deceitful device [in that it lets the screw appear to be better than it is]. … The fixed-but-adjustable nut is more 'honest' and is used to compensate for manufacturing tolerances [and to take-up wear] in the nut.

MichaelG.
30 October 2017 at 11:57 #324423
Tony Pratt 1
Participant
@tonypratt1
Again no criticism of the article but is having backlash in a cross slide screw a problem?

Tony
30 October 2017 at 12:21 #324425
Jeff Dayman
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@jeffdayman43397
Posted by Tony Pratt 1 on 30/10/2017 11:57:41:

Again no criticism of the article but is having backlash in a cross slide screw a problem?

Tony

Yes it can be, one instance being while facing the end of stock, as the tool approaches centre it can jump across the centre and drag on the wrong side. This usually messes up the finish. Also when parting, if there is any drag and resulting tool feed direction change, the tool can jump and dig in.

On my old South Bend lathe, there is a lot of wear in the cross slide screw and nut. I have tried various fixes but due to varying wear along the screw, anti-backlash tension also needs to vary along the screw. Spring type devices are semi effective and due to forces involved at the tool, a REALLY heavy spring is needed to stop movements. This results in unpleasant operation. One of these days I will make a new screw and wider nut in better materials and better fit, or fit a good quality hardened ball screw unit, and maybe that will fix it forever. JD
30 October 2017 at 12:54 #324434
Bazyle
Participant
@bazyle
If boring is a problem you can invert the tool and work on the other side.

I don't think the spring can make the effect of following the errors in the screw worse as you'd want to follow one flank warts and all whatever the arrangement. However for occasions when consistent distance travelled is vital consider biasing against the other flank (ie pushing the crosslide in hard) as that one will be less worn.

Mostly overlooked but the well known "Know your lathe" book recommends having the tool a little above centre height (cue much whining). It's not explained but that is so that a component of the cutting force pushes the crosslide outwards to take up the slack.
30 October 2017 at 13:02 #324436
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Bazyle on 30/10/2017 12:54:41:

… I don't think the spring can make the effect of following the errors in the screw worse …

.

Just for clarity, Bazyle : I did not suggest that it would make it worse; simply that it conceals the errors.

MichaelG
30 October 2017 at 13:03 #324437
Chris Trice
Participant
@christrice43267
Depending on the force of the spring, wouldn't this promote wear in the screw and nut?
30 October 2017 at 13:13 #324442
Michael Gilligan
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@michaelgilligan61133
Posted by Chris Trice on 30/10/2017 13:03:50:

Depending on the force of the spring, wouldn't this promote wear in the screw and nut?

.

Very probably.

MichaelG.
30 October 2017 at 14:11 #324457
ega
Participant
@ega
The simple but costly solution to wear in the cross slide nut and/or feedscrew is to renew one or both. The Myford nuts were relatively cheap, however, and I think may have been intended to wear more quickly than the screw.

Early in its life with me and possibly before I replaced nut and screw I fitted a bracket spacer to my S7 cross slide and it occurs to me now that this may have had the incidental effect of shifting the bulk of the movement to a less worn portion of the screw. I don't recall the specific reasoning but, obviously, the effect of the modification is to give more travel away from the operator (and less towards them). Here's a photo:

The job in the lathe is boring out the damaged end of an octagonal London pattern boxwood chisel handle in situ to receive a replacement knob in the same material; blade in 4 jaw, handle in "cathead" and cathead in fixed steady.

Edited By ega on 30/10/2017 14:11:58
30 October 2017 at 17:36 #324491
Neil Wyatt
Moderator
@neilwyatt
Posted by Michael Gilligan on 30/10/2017 13:02:36:

Posted by Bazyle on 30/10/2017 12:54:41:

… I don't think the spring can make the effect of following the errors in the screw worse …

.

Just for clarity, Bazyle : I did not suggest that it would make it worse; simply that it conceals the errors.

MichaelG

If removal of backlash rather than absolute accuracy is the intent you could equally argue that a sprung solution is better.

Neil
30 October 2017 at 18:32 #324499
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Wyatt on 30/10/2017 17:36:42:

If removal of backlash rather than absolute accuracy is the intent you could equally argue that a sprung solution is better.

Neil

.

Indeed I could … but I chose to start the ball rolling by discussing the aspect that most interests me.

MichaelG.
30 October 2017 at 18:49 #324508
Bazyle
Participant
@bazyle
ega that's a nice bit of lateral thinking with the chisel. Worth including in the hints and tips archive I think.
30 October 2017 at 20:13 #324515
norm norton
Participant
@normnorton75434
….start the ball rolling…. Cheeky monkey, I thought the OP might have done that

But no one has responded to my original question on whether the sprung loaded cross slide is a reliable (accurate / safe) device when boring. Jeff suggests that a REALLY strong spring is needed when facing. If that is correct for boring then the whole concept is not viable.

Norm
30 October 2017 at 20:14 #324516
Robin
Participant
@robin
I suppose it depends on your application and the forces involved. You don't have to go the full Belleville if a few pounds force is all it needs.

To get a constant force, how about lifting a weight over a pulley? Newton still beats Hook if you avoid major accelerations.
30 October 2017 at 20:36 #324526
Chris Evans 6
Participant
@chrisevans6
Commercially available lead screw and nuts are cheap. A couple of years ago I bought a length of lead screw and two bronze nuts. enough screw to make three cross slide feed screws and mill the round nuts to fit the lathe. Total spend was under £70 and I have a spare sitting on a shelf with a new nut plus enough spare screw to make another but I won't live that long to wear them out.

Edited By Chris Evans 6 on 30/10/2017 20:36:49
30 October 2017 at 22:27 #324548
Michael Gilligan
Participant
@michaelgilligan61133
Posted by norm norton on 30/10/2017 20:13:27:

….start the ball rolling…. Cheeky monkey, I thought the OP might have done that

.

Sorry, norm … No cheek intended : I thought the OP 'placed the ball' and the responses 'rolled' it.

MichaelG.
30 October 2017 at 22:45 #324551
duncan webster 1
Participant
@duncanwebster1
On the rare occasions that backlash in the cross slide feed screw matters, I simply hang on to the toolpost and lean back. End of problem

Edited By duncan webster on 30/10/2017 22:46:08
30 October 2017 at 23:15 #324557
ega
Participant
@ega
Bazyle:

Thanks for that. This was a job for a friend who wanted to keep the original handle; had it been a replacement job I would have taken the more straightforward course of splitting off the old handle and making a new one.
31 October 2017 at 02:14 #324559
Chris Trice
Participant
@christrice43267
I had a job once that was very delicate being machined on my previous fairly worn Myford and to remove the backlash, I hooked a piece of bungee onto the cross slide and attached the other end to the wall behind the lathe. The tension was enough to keep any play out of the equation.
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